1. Field of the Invention
This invention is general relates to photographic camera apparatus, and, in particular, to scene light detecting apparatus for use with an automatic camera of the type which has a distinct ambient exposure mode of operation and a distinct flash exposure mode of operation in which an artificial light source is utilized to illuminate the scene.
2. Description of the Prior Art
Built-in light detecting devices which form an integral part of an automatic camera's exposure control arrangement are well known to those skilled in the photographic arts. Such light detecting devices generally consist of one or more photovoltaic or photoresistive type transducers associated with an optical system so that light from a preselected area of the scene to be photographed can be directed onto the photosensitive surface(s) of the transducer(s). An electrical output signal indicative of the intensity of the brightnesses of the various objects located in the preselected area of the scene is derived from the transducer(s) and is thereafter generally utilized to control the exposure delivered to the film in accordance with the speed of the film's photosensitive material and the known performance characteristics of the other elements which comprise the exposure control arrangement. The electrical output signal may be used prior to actual exposure to automatically adjust the exposure settings of the camera or may be used after an exposure cycle is initiated to terminate the cycle upon satisfaction of a predetermined exposure condition.
The preselected area of the scene depends on the "angle of acceptance" of the light detecting device; the "angle of acceptance" meaning the solid angle of the cone of light received by the light detecting device. Thus, if light from a particular scene object is to have an influence on the magnitude of the output signal of the light detecting device, that object must be located within the device's angle of acceptance, i.e., the object must be "seen" by the device. It is apparent therefore that the angle of acceptance of such light detecting devices can be used as a means for controlling what the exposure will be in the sense that it can be aimed at a certain area of the scene which is considered important in preference to another area of the scene which may not be considered quite as important.
However, what the angle of acceptance should be for a particular light detecting device depends on the kinds of scenes it will probably be used to measure and the type of lighting which is used to illuminate those scenes. Consider, for example, a horizontal landscape illuminated by skylight or sunlight. With this type of scene and lighting conditions, it is generally desirable to have a light detecting device which looks generally downwardly to exclude the sky whose influence, if considered, would tend to cause the ground details to be underexposed. As another example, consider a portrait scene illuminated with an artificial light source. In this type scene, it is generally desirable to have the light detecting device "look" straight ahead or slightly upwardly so as to receive substantially all the light reflected from the subject's face thereby exposing for proper fleshtones.
Those skilled in the art have recognized the important role that the angle of acceptance of such light detecting devices plays in controlling exposure and have described a number of light detecting devices by which the importance of different areas of a scene can be established via the device's angle of acceptance. For example, in U.S. Pat. No. 3,511,142 issued to Conrad H. Biber on May 12, 1970 and entitled "Exposure Control Means", there is described an exposure control system which has a parameter which is modified in response to the attachment of a flash unit to a camera in which the exposure control system is incorporated. Specifically, attachment of the flash unit shifts a movable element into operative position relative to four photocells such that the fields of view (angles of acceptance) of the photocells are substantially congruent, each covering substantially the angular field of view of the camera. Under ambient lighting conditions (i.e., without a flash unit attached) the movable element is operatively positioned relative to the photocells so that each photocell is provided with a smaller angle of acceptance each of which is aimed at a different portion of the scene being photographed. With this arrangement, the angle of acceptance of each photocell is changed from a small solid angle when used in the ambient mode to a large solid angle when used in the flash mode thereby affecting a change in the sensitivity of each photocell in accordance with the size of its angle of acceptance.
Another example is described in U.S. Pat. No. 3,232,192 issued to Allen G. Stimpson on February 1, 1966 and entitled "Photographic Exposure Measuring Device". Here an exposure control system is described which utilizes a plurality of photocells one of which is positioned to measure the intensity of skylight and others each having a different acceptance angle for viewing a correspondingly different zone of the scene to be photographed. A pair of the photocells are fixedly aimed at different selected zones of the scene and their individual angles of acceptance, when combined, cover substantially all of the scene as defined by the angular field of view of the camera. No provision is made for preferentially exposing different zones of the scene by changing the angular direction in which the photocells are aimed at the scene. Instead individual zones of the scene are given preferential treatment by providing the photocells with different sensitivities and combining their outputs in an electrical arrangement by which a single output is generated to indicate or automatically regulate proper exposure.
It is a primary object of the present invention to provide a light detecting apparatus for use with an automatic camera to control exposure under both ambient and flash illumination conditions.
Another object of the present invention is to provide light detecting apparatus which has a predetermined angle of acceptance which may be aimed in different angular directions at a photographic scene without changing the angular size of angle of acceptance.
Another object of the present invention is to provide light detecting apparatus with a predetermined angle of acceptance for use with an automatic camera of the type having distinct ambient and flash exposure modes of operation and to provide an arrangement by which the angle of acceptance of the apparatus is normally aimed in one angular direction while the camera is in its ambient exposure mode of operation and is automatically aimed in another angular direction by inserting an artificial lighting assembly into the camera.
Other objects of the invention will in part be obvious and will in part appear hereinafter. The invention accordingly comprises the apparatus possessing the construction, combination of elements, and arrangement of parts which are exemplified in the following detailed disclosure.